Question: Divide the following complex numbers: $\dfrac{10(\cos(\frac{3}{2}\pi) + i \sin(\frac{3}{2}\pi))}{5(\cos(\frac{7}{4}\pi) + i \sin(\frac{7}{4}\pi))}$ (The dividend is plotted in blue and the divisor in plotted in green. Your current answer will be plotted orange.)
Explanation: Dividing complex numbers in polar forms can be done by dividing the radii and subtracting the angles. The first number ( $10(\cos(\frac{3}{2}\pi) + i \sin(\frac{3}{2}\pi))$ ) has angle $\frac{3}{2}\pi$ and radius 10. The second number ( $5(\cos(\frac{7}{4}\pi) + i \sin(\frac{7}{4}\pi))$ ) has angle $\frac{7}{4}\pi$ and radius 5. The radius of the result will be $\frac{10}{5}$ , which is 2. The difference of the angles is $\frac{3}{2}\pi - \frac{7}{4}\pi = -\frac{1}{4}\pi$ The angle $-\frac{1}{4}\pi$ is negative. A complex number goes a full circle if its angle is increased by $2 \pi$ , so it goes back to itself. Because of that, angles of complex numbers are convenient to keep between $0$ and $2 \pi$ $-\frac{1}{4}\pi + 2 \pi = \frac{7}{4}\pi$ The radius of the result is $2$ and the angle of the result is $\frac{7}{4}\pi$.